Orthogonal frequency-division multiplexing (OFDM) is a modulation scheme where data is encoded in multiple carrier frequencies. For years OFDM has been getting a lot of attention for wireless and wired communications because of its high spectral efficiency and its ability to combat ISI and channel delay with the addition of guard interval and cyclic prefix. Recently, OFDM has gained a lot of attention in powerline communications, particularly in the sub 500 kHz frequency band. There are many emerging standards for communicating over the available alternating current and direct current power lines using the low frequency band of less than 500 kHz. These emerging standards find their applications in Automatic Meter Reading (AMR), Advanced Metering Infrastructure (AMI), Solar Panels, Electric Vehicle charging stations and other industrial monitoring and control applications. Particularly, in US, Japan and Asia, the existing regulations pave the way for transmission across all the frequency band around 500 KHz. Moreover, in metering application, there is a requirement to be able to cross Medium Voltage (MV) transformer in the case of isolated meters. Isolated meters are in rural and sparsely populated areas where only a few meters, are connected to MV transformer and in order for PLC to be economically viable crossing a transformer is a requirement. The channel analysis performed in US shows that there are many channels where only a very narrow portion of the channel is available for communications. The same channel behavior has been observed in Japan and China. Specifically, in cases where only a narrow portion of the channel has good SINR (signal to interference and noise ratio), the synchronization is very difficult or even impossible, since usually a wideband time domain signal is used as a preamble.
In view of the aforementioned limitations, the present invention provides an effective way of digital communication over powerline and other media on channels where only small part(s) of the channel are suitable for communication, while still taking advantage of the OFDM modulation scheme.